1. Field of the Invention
The present invention relates to a method for adjusting sensor output gain for removing a suppressing periodic error signal components in the output of sensors provided with multiple pickup sensors used for sensing rotational position of a rotating shaft, the position of a member moving linearly, velocity, acceleration, and so forth.
2. Prior Art Description
Accurate sensing of physical quantities associated with rotational or linear motion (such as position, velocity, acceleration, torque, etc.) plays an important role in the practical application of measurement and control technology. Particularly in the case of rotary motion, while it depends on the sensor principle involved, periodic error signals are a frequent occurrence. For example, when a pickup sensor is placed at one point for sensing the angle of a rotating shaft, or velocity or transmission torque, if there is shaft eccentricity and the sensitivity of the sensor depends on the distance from the shaft, rotation of the shaft is accompanied by the generation of periodic error signals in the output of the sensor.
The usual method of compensating for such error signals is to position a pair of identical pickups symmetrically with respect to the shaft and utilize the phase opposition of the two error signals to cancel out the error signals. However, the fact that the characteristics of the pickups do not always perfectly coincide, and that there is positional error and shaft roundness error, results in a situation that is not ideal. As such, it becomes impossible to perfectly cancel out error signals.
The present inventors encountered this type of problem when conducting research into the sensing of torque from a wave gear type reduction gear system. When using magnetostriction type torque sensors, we found that the problem of how to remove error signals in optical type rotary angular acceleration sensors, for example, had not been resolved. The application of Karman filters has been proposed as a periodic error signal compensation method, but from a practical standpoint the lengthy computation time involved makes the method problematical.
In view of the above, an object of the present invention is to provide a method of compensating periodic signals in sensor output that is able to readily remove periodic error signals in rotary and linear type sensors.
To attain the above object, the present invention provides a method of compensating periodic error signals in sensor output, said method comprising obtaining a sum signal from sensing outputs of M sensor elements (where M is a positive integer); obtaining amplitude and phase of N (N is a positive integer) frequency components included in the sum signal; taking aij as sensing output amplitude of the jth (j=1 to N) sensor element at the ith (i=1 to N) frequency component, xcfx86ij as phase angle and kj as sensing output gain adjustment coefficient, obtaining adjustment coefficient kj for each sensor output by the simultaneous equation                                                         [                                                                                                                  a                        ij                                            ⁢                      cos                      ⁢                                              xe2x80x83                                            ⁢                                              φ                        ij                                                                                                                                                                                a                        ij                                            ⁢                      sin                      ⁢                                              xe2x80x83                                            ⁢                                              φ                        ij                                                                                                        ]                                      (                              2                ⁢                N                xc3x97                M                            )                                ⁢                                    {                              k                j                            }                                      (              M              )                                      =        0                            (        7        )            
ensuring that a sum signal level obtained by summing a pre-adjustment output of each sensor element multiplied by the gain adjustment coefficient kj equals a sum signal level obtained by summing unmodified outputs of said sensors, by obtaining a gain adjustment coefficient kj for each sensor output by using a scaling coefficient C obtained by                     C        =                  M                                    ∑                              j                =                1                            M                        ⁢                          k              j                                                          (        12        )            
to perform pre-adjustment scaling of each gain adjustment coefficient kj, and using each adjustment gain kj thus obtained to adjust a gain of each sensor output.
Instead of the simultaneous equation, N frequency components can be removed or minimized by using a gain adjustment coefficient obtained for each sensor output by repeating for each sensor output a process comprising changing an output gain of one sensor in small increments while maintaining output gains of other sensors at a constant level.
Next, the present invention provides a gain adjustment method for maximizing a specific frequency component in sensor output, said method comprising obtaining a sum signal from sensing outputs of M sensor elements; calculating amplitude of specific frequency components from the sum signal; obtaining the sensor output gains at which the specific frequency components are maximized by repeating for each sensor output a process comprising changing the output gain of one sensor in small increments while maintaining output gains of other sensors at a constant level; ensuring that a sum signal level obtained by summing the outputs of the sensor elements each multiplied by the calculated gain equals a sum signal level obtained by summing unmodified outputs of said sensors, by obtaining an adjustment gain for each sensor output by using scaling to adjust each calculated gain; and using each adjustment gain thus obtained to adjust the gain of each sensor output signal to generate a sum signal in which said frequency components are maximized.
The present invention also provides a gain adjustment method for minimizing a specific frequency component in sensor output, said method comprising: obtaining a sum signal from sensing output of M sensor elements; obtaining a peak-to-peak amplitude of the sum signal; obtaining the sensor output gains that give the minimum peak-to-peak amplitude of the sum signal by repeating for each sensor output a process comprising changing the output gain of one sensor in small increments while maintaining the output gains of the other sensors at a constant level; ensuring that a sum signal level obtained by summing the outputs of the sensor elements each multiplied by the calculated gain equals a sum signal level obtained by summing unmodified outputs of said sensors, by obtaining an adjustment gain for each sensor output by using scaling to adjust each calculated gain; and using each adjustment gain thus obtained to adjust the gain of each sensor output signal to generate a sensing signal in which there is minimum peak-to-peak amplitude of the sum signal of the sensor outputs.
Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and following detailed description of the invention.